This invention relates to the use of green liquor dregs and slaker grits as part of the aggregate in asphalt concrete pavement.
Green liquor dregs and slaker grits are waste products from the pulp and paper process. Approximately 6,000 to 8,000 cubic yards of the waste material are produced annually and presently discarded in onsite landfills. An alternative use for the waste is desirable because of the high cost of landfilling and the limited availability of landfill areas.
Green liquor dregs are unburned carbon and inorganic solids that result when a smelt is mixed with water. The material is insoluble in water.
Slaker grits are resulting particles that do not react in the slaking process when green liquor and quick lime are mixed under high temperatures and violent agitation to form a slaked lime.
The dregs are removed from the green liquor using a precoat filter with a lime precoat. Green liquor dregs are then scraped from the precoat filter and contain lime, unburned carbon and inorganic solids. The green liquor dregs are primarily calcium and iron compounds, and the slaker grits are predominantly calcium oxide (quick lime). Both of these materials have been characterized as non-hazardous.
Hot mix asphalt concrete paving aggregate compositions usually are composed of a fines fraction, an aggregate crushed rock component, and oil.
The fines fraction is traditionally a fine sand material which can pass through a two hundred mesh screen.
The aggregate component of the mix is traditionally a crushed rock composed of 1/2 to 1/4 sized material and 1/4- sized material and forms the bulk of the composition.
Addition of the oil creates the slurry and completes the asphalt composition.
It is an objective of the present invention to find an alternative use for green liquor dregs and slaker grits waste products.
It is a further object of the present invention to free up space in landfill areas.
It is a further object of the present invention to substitute the fines fraction component of the hot mix asphalt aggregate paving composition with the green liquor dregs and slaker grits waste products.
It is a further object of the unique aggregate composition embodying the invention to obviate the need to add additional anti-stripping agents or additional fines at completion of the composition.